Interface implemented by an MBean that emits Notifications. It
allows a listener to be registered with the MBean as a notification
listener.

Notification dispatch

When an MBean emits a notification, it considers each listener that has been
added with addNotificationListener and not
subsequently removed with removeNotificationListener.
If a filter was provided with that listener, and if the filter's
isNotificationEnabled method returns
false, the listener is ignored. Otherwise, the listener's
handleNotification method is called with
the notification, as well as the handback object that was provided to
addNotificationListener.

If the same listener is added more than once, it is considered as many times as it was
added. It is often useful to add the same listener with different filters or handback
objects.

Implementations of this interface can differ regarding the thread in which the methods
of filters and listeners are called.

If the method call of a filter or listener throws an Exception, then that
exception should not prevent other listeners from being invoked. However, if the method
call throws an Error, then it is recommended that processing of the notification
stop at that point, and if it is possible to propagate the Error to the sender of
the notification, this should be done.

Implementations of this interface and of NotificationEmitter
should be careful about synchronization. In particular, it is not a good
idea for an implementation to hold any locks while it is calling a
listener. To deal with the possibility that the list of listeners might
change while a notification is being dispatched, a good strategy is to
use a CopyOnWriteArrayList for this list.

Method Detail

addNotificationListener

listener - The listener object which will handle the
notifications emitted by the broadcaster.

filter - The filter object. If filter is null, no
filtering will be performed before handling notifications.

handback - An opaque object to be sent back to the
listener when a notification is emitted. This object cannot be
used by the Notification broadcaster object. It should be
resent unchanged with the notification to the listener.